The file extension BKF marks backup files of the Windows backup function. BKF files are only generated under Windows NT systems (Windows NT, 2000, XP).
BKF files can contain data from an entire hard disk backup, individual partitions or individual folders. In order to access the backup function, you can right-click on any partition icon in the workstation and then choose 'Tools' -> 'Save Now'. It is also possible to get there via the Control Panel-> Performance and Maintenance-> Backup Data. If you already have a BKF file, double click.
Depending on what is in a BKF file, you should exercise caution when writing back. You should not just write back foreign BKF files, as you may be able to restore an entire partition and possibly overwrite your own partitions. In case of an unknown big BKF file you should always write back to an empty partition.
Since it is no longer possible to restore BKF files under Windows Vista or Windows 7 using the operating system function, one has to resort to commercial programs such as 'Read BKF', which also make this possible under the systems mentioned. Furthermore, there are several programs to repair BKF files.